The etiology of nausea and vomiting in pregnancy is still unknown. One possibility is that ovarian and placental hormones may play some part. The liver is the major site of metabolic inactivation of steroid hormones. In this study, 102 healthy pregnant women, of whom 62 complained of nausea, were followed throughout pregnancy. Liver function tests were performed to ascertain whether emesis gravidarum is related to impaired hepatic function. In this series, all values were within the normal ranges. Serum levels of total bilirubin and gamma-glutamyl-transferase were significantly decreased and those of total serum bile acids significantly increased in emetic women compared to nonemetic subjects. Furthermore, the metabolic load on the liver seems to follow a biphasic course as there is an apparent minimum in liver function variables in the second trimester. It is concluded that a slow adaptation to the increased hormonal load on the liver might be responsible for the condition of emesis gravidarum.